Figure 11

The model predictions for coupled intraciliary Ca²⁺ concentration and membrane potential alterations. The systems model for intraciliary Ca²⁺ concentrations, Ca²⁺ and K⁺ currents coupled with membrane potential responds to applied inward current in a dynamically diverse fashion. The dynamic mode of the ciliary system is defined by the intersection of nullclines shown on phase diagrams for three representative values of inward current, I₀. A. A small inward current, I₀, initiates the generation of a small pulse of intraciliary Ca²⁺ (B) and membrane potential (C). D. A larger inward current can shift the system into the mode of sustained oscillations of both intraciliary Ca²⁺ (E) and membrane potential (F). G. Significantly higher values of inward current shift the intersection of the null clines to a higher region with a stable solution. This leads to a switch type of response to a higher steady-state level of Ca²⁺ (H) and membrane potential (I). The model describes a novel mechanism of ciliary excitability and predicts that the ciliary system can generate either a single impulse, generate sustainable oscillations, or operate as a switch between lower and higher Ca²⁺ and membrane potential levels.